Speed limits and seat belts may have checked the rate of highway death for a while, but recent reports show that with an ever-increasing number of automobiles on the world's roads, accidents are on the upswing.

Two international conferences on the growing problem of the polluting, noisy, death-dealing automobile in industrialized countries were held in Paris recently by the U.N. Environment Program and European Ministers of Transportation.

The European ministers heard results of a survey of most industrialized countries showing that the number of persons kiled or injury in road accidents in 1975 dropped or levied off for the second year in a row.

Other reports indicated that highway death really isn't taking much of a holiday.

A report prepared by Belgium and based on the curve of the trends plus what is known so far about 1976 predicted, "the leveling off of the number of casualties, possibly even an increase, in 1976."

France already is among countries that have registered an increase in highway death so far this year.

"This is not a cheerful prospect now that we have become accustomed to a regular decline in the number of casualties," the Belgian report said. "There will be reason for disquiet about the future if governments fail to take strong action ortwith to curb any sign of laxity" on spedd limits, safety belts and other measures.

The U.N. conference agreed that speed limits brought on by booming oil prices, the introduction of seat belts and road inprovements can be credited with lowering the number of highway fatalities.

The U.N. report, prepared by the Swedish delegation, emphasized that "there is no single factor that so radically can reduce the number of victims in traffic accidents as the common use of safety belts."

France, Sweden and the United States reported that speed limits applied since the 1973 energy crisis saced tens of thousands of lives in their countries.

The transportation ministers examined these 1975 trends for highway deaths:

Downward trend: Belgium, Switzerland, the Netherlands, Canada, France.

Leveling off: West Germany, Luxembourg, Sweden, the United States, Australia.

Upward trend: Norway, Spain, Turkey, Greece.